WASHINGTON (AP) — A federal judge postponed sentencing Tuesday for Michael Flynn, President Donald Trump's former national security adviser, after warning he might be incarcerated for lying to the FBI about Russia contacts.

Prosecutors and defense lawyers had each recommended no prison time because Flynn, a former Army lieutenant general, cooperated with Justice Department special counsel Robert Mueller.

But U.S. District Court Judge Emmet Sullivan asked prosecutors whether Flynn's crime amounted to treason. Prosecutors said they hadn't brought such charges.

Sullivan also warned that he may consider sentencing Flynn to “a term of incarceration." Sullivan set a status report in March.

Flynn faces a maximum punishment of five years in prison, three years of supervised release and a $250,000 fine.

In requesting the postponement, Flynn attorney Robert Kelner said his “client has held nothing back” in cooperating with prosecutors. But Kelner acknowledged the judge’s earlier cautions about proceeding to sentencing while Flynn’s cooperation was likely not yet complete.

Kelner said Flynn would likely be called to testify at future trials of two former business associates accused of illegal lobbying on behalf of the Turkish government.

“I’m not promising anything,” Sullivan told Kelner. “The court was just being upfront with you.”

Prosecutor Brandon Van Grack said the government’s recommendation for leniency was warranted, saying that Flynn had “taken full responsibility for his action.”

Prosecutors said it was possible Flynn's further assistance would be needed in ongoing investigations.

As part of his plea, Flynn also had admitted to lying about Turkish lobbying and research work. He belatedly registered with the Justice Department as a foreign agent for the work weeks after he left the White House.

Flynn, accompanied by his wife, left the the courthouse, walking through a gantlet of protesters to a waiting car without comment.

The decision to postpone sentencing came after Sullivan ordered a 15-minute recess, to allow Flynn to confer with his lawyers.

“This is a very serious offense,” Sullivan said, noting that Flynn made the false statements to the FBI on “the premises of the White House.”

But after the break, Sullivan said that he had not meant to imply that Flynn had committed treason when he earlier asked prosecutors whether they had considered bringing such an offense.

“Don’t read too much into my questions,” the judge told the court.

The sentencing was postponed after Flynn's defense lawyers filed a memo that agreed with prosecutors that deserved no prison time, but offered a new account of the Jan. 24, 2017, interview with FBI agents.

Flynn gave the interview without a lawyer present and lied about his contacts with Russia ambassador Sergey Kislyak. Before the interview, his attorneys said, FBI officials had decided that they would not warn Flynn about the criminal consequences for lying to federal agents.

"One of the agents reported that General Flynn was 'unguarded' during the interview and 'clearly saw the FBI agents as allies,' " the Flynn document stated.